module 5

• why do multicellular organisms need communication systems?

  so they can respond to changes in the internal and external environment + coordinate the activities of different organs.responses can be behavioural or physiological
• how does responding to the environment help organisms survive?

  • increase chance of survival by responding to changes in external environment e.g by avoiding harmful environments (too hot/cold)
  • respond to changes in internal environment to make sure conditions are optimal for their metabolism
• what factors do cells need to keep constant?

  • conc. of chemicals e.g glucose and sodium
  • pH
  • water potential
  • temperature
  • low levels of toxins e.g urea
  • levels of gases
• why is it so important to maintain core body temperature at around 37 degree celsius?

  temperature affects enzyme activity and enzymes control the role of metabolic reactions, when temperature too high enzymes tertiary structure breaks and the active site is changed - denatured, when temperature is too low the enzyme activity is reduced and slows the rate of metabolic reactions
• which molecules are used to transport signals over long distances between cells?

  hormones which are transported in the blood, target cells have cell surface receptors allow cells to recognise the hormones
• which type of hormone is lipid soluble steroid or non-steroid?

  steroid
• which property of non-steroid hormones stops them passing through the cell membrane?

  hydrophilic
• if a response is slow, which messenger system most likely transmitted it?

  hormonal
• if a response is short-lived which messanger system most likely transmitted it?

  nervous
• if a response has a permanent and irreversible effect, which messenger system most likely transmitted it?

  hormonal
• what is homeostasis?


  the maintaining of a constant internal environment in a constant or steady state despite any changes in the external environment
• what is negative feedback?


  a mechanism that counteracts changes (in internal conditions when the changes cause the shift away from the normal), ensures optimum internal conditions are maintained
• what is positive feedback?


  the process in the effectors increase an change detected by the receptors, not used in homeostasis because doesn't keep environment constant
• Blood clot formation


  1. Platelets become activated and release chemical

  2. More platelets triggered

  3. Blood clot formed

  4. Ends in negative feedback when body detects formed blood clot
• Control of ovulation


  1. Follicles stimulate oestrogen production

  2. Stimulates more follicle cells to develop

  3. Process ends in negative feedback when LSH stops maturation
• Breast-feeding


  1. Suckling stimulates nerve endings in nipple

  2. Stimuli carried to hypothalamus

  3. Hypothalamus produces oxytocin

  4. Oxytocin stimulates milk production

  5. If suckling stimulus not strong, not as much oxytocin produced, not as much milk produced
• Birth


  1. Head of baby presses against cervix

  2. Stimulates production of oxytocin

  3. Oxytocin stimulates uterus to contract

  4. Pushes babies head harder against cervix

  5. Triggers more oxytocin
• what are changes in internal and external environments known as?

  stimulu
• ectotherm


  organisms that do not control their body temperature internally, their body temperature fluctuates with the environment, they can't increase respiration rate to generate heat e.g. reptiles, fish
• endotherm


  organisms that can control its body temperature internally, can generate heat via exergonic reactions
• why do many ectotherms living in water not need to thermoregulate?

  water has a high heat capacity means the temperature of their environment does not change much
• why is living on land problematic for an ectotherm?

  the temperature of air can vary a lot e.g. different seasons
• how do ectotherms control their body temperatures?

  changing behaviour
• how do ectotherms increase the radiation they absorb from the sun?

  • bask in sun
  • orientate body so max surface area is exposed to the sun
  • conduction → press body against warm ground
  • exothermic metabolic reactions
• how do ectotherms recduce the radiation they absorb from the sun?

  • shelter from sun
  • press body against something cool
  • orientate so min surface area exposed
  • minimise movements to reduce metabolic heat generated
• advantages of ectotherms

  • less food used for respiration hence they need to find less food
  • a greater proportion of their energy can be used on growth
• disadvantages of ectotherms

  • less active in cooler temperatures hence at great risk of predation and also need to the day of by basking in the sun.
  • aren't capable of activity during winter hence need large food stores.
• advantages of endotherms

  • a constant temperature regardless of the environment
  • active even in times of low temperatures
  • ability to inhabit colder environments
• disadvantages of endotherms

  • significant amount of energy used to maintain body temperature
  • more food required (need to spend a lot of time eating)
  • less energy used for growth
• what are some physiological responses of ectotherms to warming?

  • dark colours in colder climates to absorb more heat radiation
  • some ectotherms can alter heart rate to increase or decrease metabolic rate
• what do peripheral temperature receptors do and why?

  we have receptors in our skin which detect surface temperature before it can affect the core body temperature by sending nerve impulses to the thermoregulartory centre of the hypothalamus
• how does shivering increase body heat?

  more heat is produced from increased respiration
• how do adrenaline and thyroxine increase body heat?

  increased metabolism
• how does sweating reduce body temperature?

  when sweat evaporates it takes heat from the body
• how is the temperature of the blood detected?

  as the blood flows past the thermoregulatory centre (TRC) of the hypothalamus, the TRC then detects whether the temp. of the blood is above or below normal. If so it carries out a response by negative feedback to get the blood back to normal
• temperature rise is detected by...

  ...thermoreceptors in the thermoregulatory centre in the hypothalamus and peripheral receptors in the skin
• what are physiological adaptations of endotherms to cool down?

  • vasodilation
  • increased sweating: sweat glands all over body, as sweat evaporates from the surface of the skin, heat is lost, cooling the blood
  • reducing insulating effect of hairs/feathers: hairs/feathers are flat. Less air trapped hence less insulation
  • panting: panting increases, losing heat as water evaporates bc some animals can't sweat
  • liver cells: rate of metabolism is reduced hence less exogenic reactions occur
• what are physiological adaptations of endotherms to warm up?

  • vasoconstriction
  • decreased sweating: some evaporation from lungs may still occur but overall water stops evaporating
  • raising body hair/feathers: hairs are raised hence trap air hence increased insulation
  • shivering: spontaneous involuntary contractions which generate metabolic heat by causing muscle cells to respire
  • liver cells: rate of metabolism increased hence more exogenic reactions occur
  • hormones: adrenaline and thyroxine released which increase metabolism → more heat
• what is vasodilation?


  arterioles near surface of the skin dilate which forces blood through the capillary networks close to the surface of the skin. heat lost by convection and radiation
• what is vasoconstriction?


  arterioles near surface of the skin constrict so little blood flows through the capillary networks close to skin, warm blood is kept below the surface. sphincters muscles also tighten and restrict bloods access to capillaries near surface of skin. little radiation takes place